.\" Copyright (c) 1983 Regents of the University of California.
.\" All rights reserved. The Berkeley software License Agreement
.\" specifies the terms and conditions for redistribution.
.\" @(#)fcntl.2 6.4 (Berkeley) %G%
res = fcntl(fd, cmd, arg)
provides for control over descriptors.
is a descriptor to be operated on by
Return a new descriptor as follows:
Lowest numbered available descriptor greater than or equal to
Same object references as the original descriptor.
New descriptor shares the same file pointer if the object
Same access mode (read, write or read/write).
Same file status flags (i.e., both file descriptors
share the same file status flags).
The close-on-exec flag associated with the new file descriptor
is set to remain open across
Get the close-on-exec flag associated with the file descriptor
If the low-order bit is 0, the file will remain open across
otherwise the file will be closed upon execution of
Set the close-on-exec flag associated with
Get descriptor status flags, as described below.
Set descriptor status flags.
Get the process ID or process group
currently receiving SIGIO and SIGURG
signals; process groups are returned
Set the process or process group
to receive SIGIO and SIGURG signals;
process groups are specified by supplying
is interpreted as a process ID.
The flags for the F_GETFL and F_SETFL flags are as follows:
Non-blocking I/O; if no data is available to a
call, or if a write operation would block,
the call returns -1 with the error EWOULDBLOCK.
Force each write to append at the end of file;
corresponds to the O_APPEND flag of
Enable the SIGIO signal to be sent to the process group
when I/O is possible, e.g.,
upon availability of data to be read.
Upon successful completion, the value returned depends on
F_DUPFD A new file descriptor.
F_GETFD Value of flag (only the low-order bit is defined).
F_GETOWN Value of file descriptor owner.
other Value other than \-1.
Otherwise, a value of \-1 is returned and
is set to indicate the error.
will fail if one or more of the following are true:
is not a valid open file descriptor.
is F_DUPFD and the maximum allowed number of file descriptors are currently
is negative or greater than the maximum allowable number
the process ID given as argument is not in use.
close(2), execve(2), getdtablesize(2), open(2), sigvec(2)
The asynchronous I/O facilities of FNDELAY and FASYNC
are currently available only for tty and socket operations.